Method of manufacturing brake boosters

ABSTRACT

A method of manufacturing vehicle brake boosters includes load testing a plurality of reaction discs and sorting the load-tested reaction discs into multiple, separate batches based on the load test results. A first batch of plunger plates is formed to an axial length to correspond with a first of the separate batches of reaction discs. A first batch of the vehicle brake boosters is assembled with a first one of the multiple, separate batches of reaction discs and the first batch of plunger plates to achieve a target jump-in force. A second batch of plunger plates is formed to an axial length to correspond with a second one of the separate batches of reaction discs. A second batch of the vehicle brake boosters is assembled with a second one of the multiple separate batches of reaction discs and the second batch of plunger plates to achieve the target jump-in force.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. patent applicationSer. No. 15/653,713, filed Jul. 19, 2017, which claims priority to U.S.Provisional Patent Application No. 62/363,960, filed Jul. 19, 2016, theentire contents of both of which are incorporated by reference herein.

BACKGROUND

The present invention relates to vehicle brake boosters and the methodof manufacturing. More particularly, the invention relates to a processfor controlling a booster jump-in point.

SUMMARY

The invention provides, in one embodiment, a method of manufacturing aseries of vehicle brake boosters. Each vehicle brake booster having abrake input member configured to receive a braking input force, a brakeoutput member configured to supply a braking output force in excess ofthe braking input force, an elastic reaction disc, and a plunger plate.A plurality of reaction discs are load tested for the series of vehiclebrake boosters. The load-tested reaction discs are sorted into multiple,separate batches based on the load test results. A first batch ofplunger plates for the series of vehicle brake boosters is formed to anaxial length to correspond with a first of the separate batches ofreaction discs. A first batch of the series of vehicle brake boosters isassembled with a first one of the multiple, separate batches of reactiondiscs and the first batch of plunger plates to achieve a target jump-inforce. A second batch of plunger plates for the series of vehicle brakeboosters is formed to an axial length to correspond with a second one ofthe separate batches of reaction discs. A second batch of the series ofvehicle brake boosters is assembled with a second one of the multipleseparate batches of reaction discs and the second batch of plungerplates to achieve the target jump-in force.

The invention provides, in another embodiment, a method for adapting avehicle brake booster for a desired jump-in force. An elastic reactiondisc is provided for assembly in the brake booster between an inputmember and an output member. The reaction disc is load tested. A plungerplate is selected with an axial length to complement the reaction disc,based on the load test results of the reaction disc.

The invention provides, in yet another embodiment, a method for adaptinga vehicle brake booster for a desired jump-in force. An elastic reactiondisc is mounted to a testing apparatus relative to a first plunger plateof a first axial length. The reaction disc is load tested to determine atested jump-in force based on the first axial length of the firstplunger plate. The reaction disc is paired with a second plunger plateof a second axial length to decrease the discrepancy between the testedjump-in force and the desired jump-in force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of output force versus input force for a vehicle brakebooster.

FIG. 2 is a cross-sectional view of a portion of a vehicle brake boosterincluding a reaction disc.

FIG. 3 is cross-sectional view of a load test fixture for testingreaction discs for jump-in force.

FIG. 4 is a plot of exemplary output data from the load test fixture ofFIG. 3.

FIG. 5 is a plot of a statistical distribution of the measured jump-inforce of a group of reaction discs.

FIG. 6 is an individual control chart for brake booster jump-in force,showing a reduction in upper and lower control limits.

FIGS. 7A and 7B are cross-sectional views of flat and conical typeplunger plates for the vehicle brake boosters.

FIG. 8 is a cross-sectional view illustrating a tool and process forsetting final plunger plate length by deformation.

FIGS. 9A and 9B illustrate exemplary tolerance parameters for formedplunger plates.

FIG. 10 illustrates a process cycle for the final assembly of vehiclebrake boosters.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways.

FIG. 1 illustrates a plot for output force versus input force for avehicle brake booster 20, a portion of which is shown in FIG. 2. Brakeboosters (e.g., vacuum-assisted or electrically-assisted vehicle brakeboosters) exhibit the behavior illustrated in FIG. 1 which, upon initialapplication of input force (i.e., at an input member 28 coupled to abrake actuator), does not immediately generate an output force (i.e., atan output member 30 coupled to a master cylinder). This initialcondition continues with increasing input force up until a “cut-in”input force is reached. At the cut-in input force, the brake booster 20activates and an output force is generated. The output force does notcommence gradually from zero, but rather, “jumps-in” to a non-zero forcereferred to as the jump-in output force when the input force reaches thecut-in force. After the input force exceeds the cut-in force, thepre-established relationship between input force and output forcecommences over the remainder of the operable range of increased inputforce. This may include a linear portion, having a fixed gain (i.e.,slope of output force to input force). The linear gain relationship cancontinue up until “run-out” or maximum boost, where the output force toinput force plot tapers off (i.e., slope reduction) substantially fromthe relationship established from the cut-in.

FIG. 2 illustrates a portion of the vehicle brake booster 20 incross-section, and only one half is shown as the components can besymmetrical about a central axis A. The booster 20 includes an inputmember 28 configured to receive a braking input force for boosting bythe booster 20. The input force and the additional boost force areconveyed to an output member or pushrod 30 which may be coupled to amaster cylinder input for actuating one or more hydraulic brake devices.The booster 20 can be divided into separate chambers, both of which canbe substantially evacuated of air such that a vacuum condition existsduring normal running operation when a brake input is not received bythe input member 28. When the input member 28 is actuated, air atatmospheric pressure is allowed to enter only one of the chambers toprovide boosting of the input force to a higher force at the outputpushrod 30. However, alternative suitable boosting schemes may besubstituted in some aspects of the invention.

Between the input member 28 and the output pushrod 30, a reaction disc36 and a plunger plate 40 are provided in contact with one another. Thereaction disc 36 and the plunger plate 40 are wholly or predominantlyresponsible for determining the initial behavior, including the jump-inforce, of the booster 20. The reaction disc 36 can be constructed of aresilient or elastic material (e.g., rubber) that is subject todeformation during operation of the booster 20 as the reaction disc 36is pressed upon by an end surface of the plunger plate 40. The plungerplate 40 can be constructed of metal or another relatively rigidmaterial that is not subject to deformation during operation of thebooster 20.

As shown in FIG. 3, a load testing apparatus 60 is provided forperforming a load test on the reaction disc 36 and the plunger plate 40.The load testing apparatus 60 includes an upper fixture 62 thatsimulates the output pushrod 30, and a lower fixture 64 that includes asensor (e.g., load cell) to measure the jump-in force. The reaction disc36 and the plunger plate 40 are interposed between the upper and lowerfixtures 62, 64. The reaction disc 36 and the plunger plate 40 may be atleast partially received within a valve body 68. The plunger plate 40may be a designated component having a known axial length and used withthe load testing apparatus 60 for testing an entire group of reactiondiscs 36 before the reaction discs 36 are supplied for assembly withrespective vehicle brake boosters 20. Once a load test is performed fora particular reaction disc 36, the jump-in force provided thereby isnoted, for example, according to the graph shown in FIG. 4. In theillustrated non-limiting example, points A and B are data points fromthe load test, plotted as input force versus output force. The linebetween points A and B is extrapolated to the y-axis, where point C isdefined. Point C represents the measured jump-in force for the reactiondisc 36. In the illustrated example, the ratio of output force to inputforce is 11.75:1 based on the slope of the line between measured pointsA and B and the jump-in force is 1100.8 N.

In producing a series of vehicle brake boosters 20 on an assembly lineof a manufacturing facility to meet a consistent performance standard,the reaction discs 36 that have been load tested can first be groupedinto separate batches. In the simplest form, this may include separatingall the reaction discs 36 into a “high” group and a “low” group,according to the measured jump-in force from the load test, with thehigh group providing a jump-in force above a mean or target value, andthe low group providing a jump-in force below the mean or target value.The separate batches may include more than two groups of reaction discs36. Furthermore, some reaction discs 36 may not be within the desiredrange, and may be discarded. For example, FIG. 5 shows an exemplarystatistical distribution, including high and low outliers as determinedby a designated number of standard deviations. With the pre-sortedbatches of reaction discs 36, the assembly process for production of aseries of brake boosters 20 can be improved as discussed below. Theindividual values chart, or I-chart, of FIG. 6 shows how an existingproduction process with existing upper and lower control limits can beimproved by bringing the upper and lower control limits closer to themean value.

A tool 80 for performing a length correction process on existing plungerplates 40 is shown in FIG. 8. The tool 80 includes a press 80A and abase 80B, between which a plunger plate 40 is positioned and subjectedto a pressing load. The plunger plates 40 for the production series ofbrake boosters 20 can be of the flat type shown in FIG. 7A or theconical shape shown in FIG. 7B. Although all the plunger plates 40 areproduced in a prior process to achieve a nominal axial length L, theprocess shown in FIG. 8 with the tool 80 acts as a supplementary orfinal length correction that is based on data from the load testing ofthe reaction discs 36 so that a group or batch of plunger plates 40 canbe produced with a precisely controlled axial length that iscomplementary with a batch of the reaction discs 36 to more closelyachieve the desired target jump-in force for the brake boosters 20produced with those batches of reaction discs 36 and plungers 40. Forexample, the batch of high jump-in force reaction discs 36 can be slatedfor first production, and the corresponding batch of plunger plates 40can be processed through the tool 80 (i.e., plastically deformed toreduce the axial length L). The axial length L of the plunger plates 40for the batch of high jump-in force reaction discs 36 can be set to arelatively low value. Then, the batch of low jump-in force reactiondiscs 36 can be slated for second production, and the correspondingbatch of plunger plates 40 can be processed through the tool 80 (i.e.,plastically deformed to reduce the axial length L). The axial length Lof the plunger plates 40 for the batch of low jump-in force reactiondiscs 36 can be set to a relatively high value compared to the finalaxial length of the plunger plates 40 for the high jump-in forcereaction discs 36. By having the axial length L of the plunger plates 40tailored to a specific batch of reaction discs 36, complementarycomponent pairs are generated that are substantially more uniform injump-in characteristics within the vehicle brake boosters 20. Saidanother way, the production of vehicle brake boosters 20 can includedeforming a first plunger plate 40 more than a second plunger plate 40,where the first plunger plate 40 is paired with a reaction disc 36tested for relatively high jump-in force and the second plunger plate 40is paired with a reaction disc 36 tested for relatively low jump-inforce.

In the case of a conical shaped plunger plate 40 as shown in FIG. 7B,the deforming operation with the tool 80 is designed not to deform theactive conical surface of the plunger plate 40. An axially-centrallylocated reduced diameter protruding portion 84 of the plunger plate 40may be checked for conformance to certain tolerance thresholds after thepressing with the tool 80. For example, in some cases, a minimum heightH1 must be maintained between the reduced diameter protruding portion 84and a radially outer flange portion 88 as shown in FIG. 9A. Further, adiameter of the protruding portion 84 may be confirmed to be no greaterthan a predetermined maximum value as shown in FIG. 9B. An outsidediameter of the plunger plate 40 may be checked to ensure that it doesnot expand more than a predetermined maximum value.

The process cycle diagram of FIG. 10 illustrates how the reaction discs36 are load tested and grouped in separate groups at a first step 100.Thereafter, at step 102, the plunger plate adjustment or deformationstep with the pressing tool 80 is performed. As noted above, the plungerplate adjustment may include pressing an entire batch of plunger plates40 to a first axial length L to complement an entire batch of reactiondiscs 36 that are grouped together based on their load test results.Thereafter, the pressing tool 80 can be adjusted to press a second batchof plunger plates 40 to a second, different axial length L to complementa separate batch of reaction discs 36 that are grouped together based ontheir load test results. At step 104, the vehicle brake boosters 20 areassembled, including the paired reaction discs 36 and plunger plates 40.The vehicle brake boosters 20 can be assembled in batch form accordingto the batches of reaction discs 36, or the brake boosters 20 can beassembled in a series including interspersed first and second batchreaction discs 36 as long as the selected reaction discs 36 are pairedwith the plunger plates 40 of the corresponding batch. At step 106, aperformance test is carried on the assembled vehicle brake boosters 20.At least part of the test may involve checking the jump-in force. Basedon the test results at step 106, any necessary correction feedback forthe plunger plate length setting can be sent to the tool 80, orcontroller thereof, at step 108. In some constructions, the process mayinclude selecting a specific plunger plate 40 according to a knownlength parameter (e.g., from “long” or “short” variants) to accompanyeach given reaction disc 36, depending on whether that reaction disc 36tested high or low in the load test. It is also noted that the series ofbrake boosters need not be assembled according to batch production, andin some embodiments may take the form of a single piece flow process. Aslong as the load tested reaction discs are tracked through the process,the brake booster assembly process can include plunger length selectionfor each brake booster 20 according to the load test results of thegiven reaction disc 36 supplied for that brake booster 20.

In some aspects, the invention enables a significant improvement in thestatistical variation of brake booster jump-in characteristic, withoutrequiring any significant revision to improve the statistical variationin the manufacture of existing reaction discs, despite that the reactiondiscs account for the majority of the jump-in variation. Production ofbrake boosters with more consistent jump-in force results in vehicleproduction having more consistency in brake pedal feel fromvehicle-to-vehicle.

Various features and advantages of the invention are set forth in thefollowing claims.

What is claimed is:
 1. A method for adapting a vehicle brake booster fora desired jump-in force, the method comprising: providing an elasticreaction disc for assembly in the brake booster between an input memberand an output member; load testing the reaction disc; and selecting aplunger plate with an axial length to complement the reaction disc,based on the load test results of the reaction disc.
 2. The method ofclaim 1, wherein selecting the plunger plate includes selecting aplunger plate pre-formed with a predetermined axial length thatcomplements the reaction disc to achieve the desired jump-in force. 3.The method of claim 1, wherein selecting the plunger plate includespressing the plunger plate on a brake booster assembly line to achieve adesired axial length that complements the reaction disc to achieve thedesired jump-in force.
 4. The method of claim 1, wherein load testingthe reaction disc includes measuring an output force in response to aninput force.
 5. The method of claim 1, further comprising assembling thevehicle brake booster by locating the reaction disc and the secondplunger plate relative to the brake input member and the brake outputmember of the vehicle brake booster.
 6. The method of claim 1, whereinthe axial length of the plunger plate complements an elasticity of thereaction disc to produce the desired jump in-force.
 7. A method foradapting a vehicle brake booster for a desired jump-in force, the methodcomprising: mounting an elastic reaction disc to a testing apparatusrelative to a first plunger plate of a first axial length; load testingthe reaction disc to determine a tested jump-in force based on the firstaxial length of the first plunger plate; pairing the reaction disc witha second plunger plate of a second axial length to decrease adiscrepancy between the tested jump-in force and the desired jump-inforce.
 8. The method of claim 7, further comprising pressing the secondplunger plate to achieve the second axial length.
 9. The method of claim7, further comprising assembling the vehicle brake booster by locatingthe reaction disc and the second plunger plate relative to a brake inputmember and a brake output member of the vehicle brake booster.
 10. Themethod of claim 7, wherein determining the tested jump-in force includesmeasuring an input force relative to an output force at a plurality ofinput force values and extrapolating to determine an output force at aninput force value of zero.
 11. The method of claim 7, wherein thereaction disc is a first reaction disc, the method further comprising:mounting a second elastic reaction disc to the testing apparatusrelative to the first plunger plate; load testing the second reactiondisc; and pairing the second reaction disc with a third plunger plate ofa third axial length.
 12. The method of claim 7, wherein the first axiallength is not equal to the second axial length.